A Tory attack ad featuring the slogan 'Stéphane Dion is not a leader' was released in 2007. (Fred Chartrand/Canadian Press)

A former leader of the Liberal Party of Canada blames Conservative attack ads for torpedoing his past election campaign — and he's worried it might happen again.

Stéphane Dion, who is running for re-election as an MP in the Montreal riding of Saint-Laurent-Cartierville, was the target of blistering attack ads from the federal Conservative party when he was Liberal leader.

The ads in 2007 and 2008 branded Dion as a weak leader and took aim at his environmental record. The Tories even paid to air some of the ads during a Canadian broadcast of the Super Bowl.

In an interview with CBC Radio on Friday, Dion said he believes the ads worked against him, and that Liberals must do a better job of countering them during the current election campaign.

"We failed. We failed. We tried to explain what was our plan and what kind of man I was, but we did not succeed," said Dion.

"The Conservatives are terribly effective to define the Liberal leader in a negative way. It worked for me. I don't want that to work for Mr. Ignatieff."

With the campaign past the halfway point, both the Liberals and Conservatives have recently rolled out new TV attack ads against each other.

The Conservative ads encouraging voters to think twice before voting for current Liberal leader Michael Ignatieff.

Some Tory ads have linked voting for Ignatieff with higher taxes and a "reckless" coalition that includes the Bloc Québécois.

Dion said he hopes negative campaigning does not become a model for success in Canada.

"It's why I ask everyone who believes in what we are trying to do as Liberals to work very hard because I do not want this kind of negative politics to win twice. The message will be that the way to win in Canada is to be negative," he said.

Political advertising is excluded from the Advertising Standards Canada code of advertising standards.